Educated at the abbey of Saint-Denis, Paris, Hincmar was named a royal consultant to King Louis I the Pious in 834. When King Charles the Bald of France continued him in that office (840), Hincmar incurred the hostility of Emperor Lothair Lothar I, Charles’s rival. Chosen archbishop of Reims in 845, Hincmar began an extensive reorganization of his diocese but was accused by Lothair Lothar of impropriety for having nullified the priestly ordinations of his predecessor. The synod of Soissons (853) decided in Hincmar’s favour, and in 855 he received the approbation of Pope Benedict III. Controversy with the imperial family sharpened in 860, when Hincmar, responding to the attempt of Lothair Lothar II of Lorraine to repudiate his wife, wrote De divortio Lotharii et Teutbergae (“On the Divorce of Lothair Lothar and Teutberga”), the fullest apology to that time for Christian opposition to divorce.

In 863 he deposed Rothad, bishop of Soissons, for contesting his authority but was reversed by Pope Nicholas I the Great. He did procure, however, the condemnation of his nephew, Bishop Hincmar of Laon, in a similar dispute. On the entire matter of his ecclesiastical jurisdiction, he wrote the noted Opusculum LV capitulorum (“A Brief Tract of 55 Chapters”). After Lothair Lothar died (869), he secured the succession of Charles the Bald, whom he himself crowned, despite the objections of Pope Adrian II. In 876 he again opposed the pope, whose appointment of a papal legate for Germany and Gaul he regarded as an interference with his administrative rights. He died while fleeing a Norman raid.

Hincmar’s fame also derives from his theological controversy with Gottschalk, monk of Orbais, on the doctrine of predestination. Hincmar in Ad reclusos et simplices (“To the Cloistered and Simple”) upheld the traditional distinction between divine foreknowledge and predestination and maintained that God does not damn a sinner in advance. Because of widespread criticism that such a doctrine was not biblical, Hincmar wrote De predestinatione Dei et libero arbitrio (“On God’s Predestination and Free Will”), in which he held that God cannot predestine the wicked to hell lest he be accounted the author of sin. After tedious councils at Quiercy (853) and Tuzey (860), both parties reached a reconciliation. A second theological dispute with Gottschalk concerned Hincmar’s suspicion that certain liturgical expressions on the Divine Trinity (one God in Three Persons) could be misinterpreted as meaning a multiplication of deities. He defended his strictures in the treatise Deuna et non trina deitate (c. 865; “On One and Not a Threefold Deity”). He is also credited with being one of the first to doubt the authenticity of the False Decretals, an 8th- or 9th-century collection of spurious documents supporting papal supremacy.

Hincmar’s writings are contained in the series Patrologia Latina, J.-P. Migne (ed.), vol. 125–126 (1852). A critical edition of his letters is given in Monumenta Germaniae Historica, Epistolae VIII (1935).